500 years ago is when it started. Thousands have arrived just today alone. I think you are confusing assimilation for lack of diversity which I understand and it’s amusing that we invented the whole DEI thing because diversity is way more than cultural and ethnic differences these days so really this topic as presented is sort of dated and belongs in another century. But good for the infallible scholars you cite. It’s all figured out and the US is now the least diverse country in history.